The purpose of this project is to characterize humoral immunity to the different serotypes of group B beta hemolytic streptococci (GB-BHS) in pregnant women and new born infants. Sera from normal subjects and patients with perinatal infections (endometritis, neonatal sepsis) will be studied in animal models, in vitro systems, and the enzyme-linked immunosorbent assay (ELISA). We will characterize the immunoglobulin class and determine the role of complement in the classical and/or alternative pathways in opsonization of GB-BHS. The mouse protection test will be utilized for studies of GB-BHS type I and II infections. The chick embryo will be used primarily as an animal model for GB-BHS type III infections and in comparison with the mouse system for immunity to challenge with GB-BHS, I and II. The bactericidal assay will be employed to characterize the opsonins to all serotypes, to assess the role of complement, and to determine the class of immunoglobulin following sephadex G-200 chromatography. Participation of the complement pathways will be elucidated by heat inactivation, chelation with EDTA and MgEGTA, and absorption at 0 degree. The long chain reaction will be studied as a biological correlate for the presence of antibody in human sera and to roughly differentiate the amount of capsular antigen in stock and wild-type strains of GB-BHS. The type-specific carbohydrate antigens will be purified by trichloroacetic acid extraction, and antibody will be determined by ELISA. Results in ELISA will be correlated with the in vitro assays (bactericidal and long chain reaction) and the animal models.